DESCRIPTION: This application focusses on CDC13, a gene that had previously been shown by Hartwell's laboratory to have an essential role in maintaining telomere integrity. The PI has since shown that Cdc13 is a single-strand binding protein, suggesting that the essential function of this protein is to provide a protective cap at the end of the chromosome. However, the PI has also shown that CDC13 has a role in the telomerase-mediated pathway for telomere maintenance, leading her to propose that the Cdc13 protein regulates telomerase by mediating access of this enzyme to the chromosome terminus. This proposal sets out to examine these two roles for the Cdc13 protein by a combination of genetic and biochemical techniques. The specific aims are: (1) to use three different genetic screens to look for factors that interact with CDC13 either directly or indirectly. (2) To conduct a detailed functional analysis of CDC13 via analysis of the DNA-binding domain, analysis of the telomerase-related function, and identification of conserved and/or hypomutable regions of the gene. (3) To conduct a biochemical analysis of the proposed role of the Cdc13 protein by examining whether Cdc13 and associated proteins are components of telomerase or telomeric chromatin, by characterizing the interactions between Cdc13 and the products of genes identified in aim 1, and by characterizing any enzymatic activities associated with either Cdc13 or Cdc13 interacting proteins.